1. Field of the Invention
The present invention relates to a filter for processing blood, which serves to remove undesirable components such as aggregates and leukocytes from blood. In particular, it relates to a precise and disposable filter for processing blood, to be used for removal of side-effect-causing microaggregates and leukocytes from blood transfusion-intended whole blood preparations, erythrocyte preparations, platelet preparations, blood plasma preparations and the like, and more particularly to a flexible filter wherein a resin material or the like is used as the container material.
2. Related Background of the Invention
Separation of whole blood collected from donors into blood components, such as erythrocyte preparations, platelet preparations and blood plasma preparations, and blood transfusion following their storage, is becoming a common procedure. Because the microaggregates and leukocytes present in such blood preparations are a cause of numerous blood transfusion side-effects, many methods are carried out by blood transfusion after removal of the undesirable components prior to the blood transfusion, or the use of blood transfusions from which the undesirable components have been removed following blood collection and storage.
The most common method for removing leukocytes from blood preparations involves treatment of the blood preparation using a leukocyte removal filter. Leukocyte removal filters include two types, leukocyte removal filters with flexible containers, employing as the container a material that is flexible and has excellent vapor permeability, identical or similar to one employing a filter element made of a nonwoven fabric or porous body in the bag of a blood collection separation set, and those having a filter element comprising a nonwoven fabric or porous body packed into a hard container of polycarbonate or the like.
For common treatment of blood with such leukocyte removal filters, a bag containing the blood preparation to be treated, which is connected to the blood inlet side of the filter via a blood tube, is placed at a position about 20 cm to 100 cm higher than the filter, the blood preparation passes through the filter by the action of gravity, and the filtered blood preparation is received in a collection bag connected to the blood outlet side of the filter via a blood tube. In the case of a leukocyte removal filter with a flexible container, pressure loss occurs due to the resistance of the filter element during filtering, causing the space on the filter inlet side to be at positive pressure. With a filter comprising a flexible container, the flexibility of the container causes the container to warp into a balloon shape under the positive pressure, such that the filter element presses against the container on the outlet side.
In the gap between the outlet container and filter element, on the other hand, since blood in the blood tube connected to the outlet falls by gravity and attempts to move into the bag provided for collection of the filtered blood, which is normally placed at a location 50-100 cm lower than the filter, this action produces negative pressure and the flexible container thus tends to stick to the filter element. That is, the filter element sticks to the container on the outlet side by double force, and flow of the blood is inhibited.
Relatively inexpensive hard containers such as polycarbonate, that can withstand autoclave sterilization, may be employed to prevent sticking of the filter element to the container at the outlet side. However, considering that sterilization of the entire apparatus is necessary if it is to be used for treatment of a blood preparation, packing into a hard container impairs the vapor permeability and necessitates a prolonged sterilization time. Moreover, prolonged autoclave sterilization leads to deterioration of preserved blood, and therefore filter sterilization must be followed by complicated procedures such as sterilization after connecting the blood bag, circuits and the like.